program Three;

{$APPTYPE CONSOLE}

uses
  SysUtils;

var
n, i, b:integer;

begin
  readln (n);
  b:=0;
  if (n mod 2 = 0) then
    for i:= 1 to n div 2 do
      b:= 2*i+b;
  if (n mod 2 = 1) then
    begin
      for i:= 1 to ((n+1) div 2) do
        b:= 2*i+b;
      b:=(((n+1)*(n+2)) div 2)-b-1;  
    end;
  writeln (b);
  readln;
end.
